(a) Technical Field
The present invention relates to a conjugated diene polymer end-modified with an alkoxysilane derivative. More particularly, the present invention relates to an end-modified conjugated diene polymer, wherein an alkoxysilane derivative having an ether group and a dialkylamino group is bonded as end modifier to an end of a conjugated diene polymer, which is useful as a rubber material for a tire tread owing to improved compatibility with an inorganic reinforcing agent.
(b) Background Art
Recently, researches are carried out diversely to develop high-performance rubber for environment-friendly and energy-saving high-performance tires. For development of a high-performance tire, development of a rubber satisfying the dynamic properties of low rolling resistance and high wet traction, which can have a direct effect on fuel efficiency, is essential.
In general, styrene-butadiene rubber (SBR) or butadiene rubber (BR) is used as tire rubber. They are prepared by solution polymerization or emulsion polymerization. Solution styrene-butadiene rubber (SSBR), which is prepared by solution polymerization, is prepared in an organic solvent using an organolithium initiator. Emulsion styrene-butadiene rubber (ESBR), which is prepared by emulsion polymerization, is prepared by solidifying latex which is obtained using a radical polymerization initiator. The solution polymerization method is advantageous in that not only the control of a micromolecular structure such as the vinyl structure of a conjugated diene, the block ratio styrene, etc. but also the control of the ratio and number of coupling, which can have a great effect on the physical properties of the polymer, is possible as desired. Since the polymer prepared by the solution polymerization method is relatively superior to the polymer prepared by the emulsion polymerization method in dynamic properties such as rolling resistance and wet traction, it is widely used to prepare a tire rubber. In addition, the solution polymerization method allows control of cold flow at room temperature by modifying the polymer using an organolithium initiator and an end modifier and introducing a functional group as well as improvement of dispersibility of a reinforcing agent by improving processability and binding ability during mixing with the reinforcing agent. In particular, by improving compatibility with carbon black or silica used as a reinforcing agent in a tire, the method can provide improved (tread) wear resistance, reduced rolling resistance and improved wet traction.
The existing solution polymerization methods using functional initiators or end modifiers are as follows.
U.S. Pat. No. 5,508,333 discloses a method for obtaining dynamic and mechanical properties superior to those of the existing rubber materials by modifying the end of a polymer molecule with an alkoxysilane-based compound having an epoxy group. Although the alkoxysilane-based end modifier allows introduction of a hydroxyl group to the end of the polymer, it is not easy to control the physical properties of the polymer because control of coupling ratio is impossible.
US Patent Application Publication No. 2011-0207879 discloses a method for improving processability and reducing rolling resistance by improving compatibility with carbon black using a diphenylethylene-based polymerization initiator. However, the diphenylethylene-based polymerization initiator is not suitable for preparation of an environment-friendly tire.
US Patent Application Publication No. 2010-0152369 discloses a modified rubber prepared using an alkoxysilane compound having a primary amine group with a hydrolysable group protected as an end modifier and application of a mixture of the modified rubber with silica to a tire tread. Although the rubber having the alkoxysilane end modifier introduced can improve the physical properties of a tire tread by improving hysteresis loss, control of coupling ratio is not easy and long-term storage is problematic because of high cold flow.
As described above, in spite of the consistent efforts to improve compatibility with carbon black or silica used as an inorganic reinforcing agent and dispersibility by varying initiators or end modifiers, development of a rubber for a tire with improved mechanical and dynamic properties still remains a problem.